The technology to introduce ultrasonic energy in a liquid to accelerate the liquid flow is applied to humidifiers and washers. This takes place through putting the liquid in contact with ultrasonic vibrators and propagating ultrasonic waves in the liquid.
For example, a liquid injection washer is used for cleaning of electronic components, precision machinery, etc. As shown in FIG. 2, the washer is equipped with nozzle 1 which is fixed to face gravitationally downwards, vibrator 2 which is installed on the block section which faces injection orifice 11 of the nozzle 1, and supply pipe 3 which is connected to side of the nozzle 1 to supply liquid detergent. The vibrator 2 excites the liquid detergent, which is supplied through the supply pipe 3 into the nozzle 1, so as to give the liquid an extra acceleration in addition to the acceleration provided by gravity, thus resulting in the liquid injecting itself onto a physical object. Accordingly, for washers, in order to have the ultrasonic waves operate effectively in the liquid and manifest its cleaning capacity fully, liquid contact plane 2a of the vibrator 2 must continually be in contact with the liquid at the time of excitation. If the vibrator is excited when the liquid contact plane 2a is not in contact with the liquid, not only the cleaning capacity will be inadequate but also the vibrator will vibrate excessively and reduce its life-span. If the excessive vibration continues, the vibrator will break down.
However, in actuality, air which remains in the nozzle 1 or the supply pipe 3 or an air bubble which is formed within liquid, even if the liquid is supplied adequately, is not perfectly expelled from the injection orifice 11 and remains on the liquid contact plane. Normally, because the nozzle 1 is used with the injection orifice 11 facing downwards and because the vibrator 2 is in a higher position than the injection orifice 11 and supply pipe connection orifice 10, if an air bubble remains within the nozzle 1, the air bubble cannot escape and is in continuous contact with the liquid contact plane.
For conventional liquid injection washers, to prevent the improper operation of the vibrator 2, it was necessary to stop the excitation of the vibrator 2 and turn the injection orifice 11 upwards to expel the air bubble. In this case, because expelling the air bubble after it had built up into a large quantity would be too late to prevent excessive vibration, it is necessary to expel the air bubble little by little when only small volume has formed.
However, it is difficult to detect a small quantity of air bubble and, if the excitation of the vibrator is regularly and frequently stopped to expel the air bubble, its injection efficiency is poor. Furthermore, depending on the cleaning method, there are occasions when the mixing of chemicals such as hydrofluoric acid and ammonia is required but, because an air bubble forms easily at the time of mixing the chemicals, it was not possible with conventional liquid injection washers to use with chemicals.